Older adults often struggle to communicate in adverse listening situations, especially when they must understand one talker when there are other voices in the background. Current rehabilitation of older adults with hearing loss focuses primarily on restoring audibility via hearing aids. Unfortunately, this is of limited benefit in dificult listening environments because both speech and background noise are amplified. Restoring audibility is not enough to ensure successful communication in situations where listeners must ignore the distracting speech of other talkers. The long-term goal of this research is to develop evaluation and treatment methods that focus on both the sensory and cognitive age-related changes that mediate comprehension in these situations. The proposed experiments are designed to provide vital information about why older adults experience problems in the presence of more than one talker. Past research has yielded conflicting conclusions about the relative importance of age-related peripheral/sensory factors and age-related cognitive changes in explaining deficits in speech understanding. The studies in this proposal will help to clarify tis issue by examining how listener-related factors (specifically, working memory, processing speed, attention-switching, inhibitory control, and hearing loss) interact with stimulus-related factors to create problems understanding speech in multi-talker situations. Two specific aims will be addressed: 1.) To understand why competing speech signals are so disruptive for older listeners, and how hearing loss and cognitive processing affect their ability to cope with this interference; and 2.) To determine the degree to which hearing loss and cognitive function impact speech recognition in more realistic communication situations. The proposed experiments use both established tasks (e.g., simultaneous speech-on-speech masking, ratings of effort) and innovative techniques (temporally interleaved speech, eye tracking, limitations on response time) to address these questions. The performance of middle-aged as well as older listeners will be measured in order to provide information about which functional abilities begin to decline early vs. later in the aging process. The end result of this project will be an enhanced understanding of the factors that limit older adults from fully participating in conversations in everyday listening conditions. This, in turn, may drive improvements in rehabilitative protocols that incorporate treatment of both bottom-up and top-down contributors to age-related speech understanding problems.